Segregation and recovery of naphthenic hydrocarbon concentrates



I' I' Il' I* d n i 0 mw w m s 2 Mh. D@ Wh. .0.0 Nh. A h. S .M M. E 6 lvl# m .H e u N 0, 1v m G m R M e N M GB m 2, L1 E, mm/ mv v a A c Sv a omwm m d gf E nn a Lm m R. b Q w w S A' Mmmm m. L. m fr E V. E am mm R @Am Hm v. *mv dv S RE N .M J W 1| ER OJ. Ww ,1a Dv GD Wd S n D N 3 lo. M.,WSW m/ U RF A D A| 6mm m, S W. 3 QN/ W /I M, w m ,Zn mm w w M/ mw w.. ww. m 1 w. 0 D a a .o m w, 3 w N, j w N w w E@ n w J w. Q j n S vm. w f,f u f u. w n. S /S w 9 l A .1 \.kv 1 m e 1| n lv l, m Rs n /mm mm HR. .JSQu .wv NN Q Ew Q United States Patent lO SEGREGATIN AND RECOVERYOFVNAPH- THENIC HYDROCARBON CONCENTRATES Clarence G. Gerhold, Riverside,and Donald B. Broughton, Chicago, Ill., assignors to Universal OilProducts Company, Des Plaines, Ill., a corporation of DelawareApplication `luly 12, 19754, Serial No. 442,728

11 CIEIHS. (Cl. 26o-668) This invention relates to a process forsegregating naphthenic hydrocarbons from a hydrocarbon charging stock ina solvent extraction process. More specifically, the present inventionconcerns a two-stage solvent extraction process wherein a selecthydrocarbon stream from the primary stage is employed as the chargingstock to the secondary extraction stage and a product consistingessentially of the most volatile naphthenic hydrocarbons from the feedstock is recovered from the secondary extraction stage.

It is thus one object of this invention to prepare a naphthenichydrocarbon concentrate employing a hydrocarbon mixture comprisingparaflinic, naphthenic and aromatic hydrocarbons as starting material,effecting such separation by simple and expeditious means. Anotherobject of this invention is to increase the conversion of naphthenic toaromatic hydrocarbons in a reforming process.

' In one of its embodiments the present invention relates to a processfor separating in acountercurrent solvent extraction zone a mixture ofhydrocarbons comprising parainic, naphthenic, and aromatic componentsemploying a solvent more dense than said mixture and in which thenaphthenic and aromatic components are -at least partially soluble,removing from the lower portion of said zone a primary fat solventstream, removing from the upper portion of said zone a ranate comprisingthe paranic components of said mixture, introducing said mixture intosaid zone at a point between the raflinate and fat solvent outlets ofsaid zone, vaporizing from said primary fat solvent a light overheadcomprising aromatic and naphthenic hydrocarbon components of saidmixture, subjecting at least a portion of said overhead to solventextraction in a secondary extraction zone, recovering a secondaryraflinate from said secondary zone, comprising the relatively lowmolecular weight naphthenic components of said mixture, recycling a reuxstream selected from l) a portion of said secondary ranate and (2) aportion of said light overhead to said primary extraction zone, andintroducing said reuxsinto said primary extraction zone below the inletof said mixture therein.

More specific embodiments of the invention relate to specific naphthenichydrocarbons to be recovered as products, particular process flowarrangements to accomplish one or more of the aforementioned specificobjectives, and particular operating conditions found to be mostsuitable for such objectives.

The process of this invention may be operated for the specicpurpose ofrecovering a naphthenic hydrocarbon individual or a naphthenichydrocarbon concentrate consisting essentially of a single naphthenichydrocarbon which is valuable per se as a raw material or as a startingmaterial in the preparation of other derivatives, such as naphthenicacids or aliphatic acids by oxidation thereof. The process may also beoperated to recover ice purpose of separating the unconverted naphthenesfrom the aromatic-containing product for further conversion in thereforming process to such aromatic product. In mostnaphthene-to-aromatic hydrocarbon reforming processes the conversionapproaches an equilibrium state and the reformed product, by virtue ofsuch equilibrium, contains a substantial proportion of unconvertednaphthenes. Thus, in the conversion of cyclohexane andmethylcyclopentane to benzene through the mechanism ofdehydro-isomerization of such naphthenes in a reforming reaction, theproduct effluent from the reforming reactor generally contains asignicant proportion of unconverted cyclohexane and methylcyclopentane.In the operation of such typical reforming processes a fractionrepresenting all of the unconverted naphthenes in the product isseparated from the reforming reactor effluent and recycled as feed stockto the reforming reactor for further reprocessing. Since any fractionthus separated by simple or fractional distillation contains benzene asan azeotrope with the methylcyclopentane and cyclohexane components inthe mixture, recycle of the fraction to the reforming zone without priorseparation of the benzene therefrom tends to reduce the desiredconversion of the naphthenes to benzene by virtue of the mass actioneffect of the benzene on the equilibrium in the reforming process. Byapplying the principles of the present invention, that is, by separatingthe benzene from the recycle fraction and discharging the benzene fromthe recycle fraction, thereby providing a naphthenerich recycle stream,the equilibrium is shifted in favor of the formation of benzene `fromthe recycled naphthenes when the latter is subsequently recycled to thereforming zone.

The present invention, therefore, may be operated for the alternativeobjective of either producing a naphthene concentrate which in the caseof cyclohexane may be utilized to provide the source of raw material forSubsequent conversion to by-products such as adipic acid, for example,or the separation stage may be operated in combination with a reformingprocess for the ultimate production of benzene, toluene, xylene or amixture-of two or three of these aromatics, in accordance with theaforementioned principles affecting the equilibrium conversion ofnaphthenes to aromatic hydrocarbons.

Suitable hydrocarbon mixtures utilizable as feed stocks in the presentprocess may be selected from any sourceV a product comprising a mixtureof naphthenes utilizable of hydrocarbon mixtures containing paraiinic,aromatic, and naphthenic hydrocarbon components, and most appropriatelyfrom such mixtures which normally form azeotropic or constant boilingmixtures with each other. Thus, straight run gasoline fractions whichboil over a relatively narrow boiling range and which contain C5, Csand/or C7 hydrocarbons of the paraffin, aromatic and naphthene seriesmaybe utilized as a charging stock in the present solvent extractionprocess. Since such mixtures are inherently present in the productformed from thermal or catalytic reforming processes, distillatefractions separated from the products of such reforming processesprovide one of the most suitable sources of feed stock in the presentseparation process. Thus, a fraction separated from a reformed gasolinestock and containing C6 hydrocarbons such as methylcyclopentane,cyclohexane, the normal and branched chain C6 paraflins, and benzene mayprovide a suitable charging stock in the present process. Such fractionsgenerally boil up to about C. and are separated as adistillate fraction2.84am. f

frnatths. liquid. predutotthe hydrpfsrmins@averses process. Thenaphthene orunaphthenes to be recovered from such a fraction may becyclopentane, methylcyclo- Bestens.Qryslohexane.. Artes@ Stock having,a.V higher eadrroistfmay; also4 bei` massed.. t0l the Vprecie-Ss, forth@'www f.;CyC10hxane for an alkvlvclohexane for eX- amrlc 11s/.Charassefeed stokboilins up @about 140 C., such a fractioncontainingcyclohexane, the monoandrpolymethylcyclohexanes, tolueneA and theinormal and straightfuchainCe andC7 paranls. Broad and narrow boilingrange fractions, including `higher end boiling point mixtures, may alsobe utilized, thenaphthene to be recovered generally. beingoneror morevof the lowest, molecular weight, naphthsnespressnt in` webV a mixtureThe method f Separating naphthnis hydrocarbons from `rnirwtttu'es of thesame v,withother hydrocarbo-ns provided by the present inventioninvolves a, two-stage'` solvent extraction process ,wherein the fatsolvent stream` formed dwing the solvent extractionis subjected toI astripping operation to separatea light overhead, comprising a mixturepofthe desired naphthene product and its aromatic analogsLand thereaftersubjecting-the resulting light overhead-to a secondary extraction tosegregate the naphthenes from the aromatic hydrocarbons.- The v processfor effecting such separation, comprising this invention, is furtherdescribed in the accompanying diagram which illustrates the method inconjunction with a reforming process, the combination being one of thepreferred embodirnents of the present invention.

Referring to the accompanying drawing, a suitable mixed `hydrocarbonfeedstock containing naphthenic precursors of aromatic hydrocarbons ischarged into a cornbined reforming-solvent extraction process comprisingone of the embodiments of this invention through line 1 in amountscontrolled by valvehZ and is thereafter transferred by means," of pumpk3 and, line 4 Vat a suitable hydroforming-reaction temperature andpressure into reforminglreactor 5. The desired reaction pressure,usually fromwabout SOto about A2000 p. s. i. g. is determined by thepressure developed by pump 3 and the reaction ternperature, usually vfrom about 800 to about 1200i F., is determined by the temperature atwhich the feed stock is heated in furnace 6 which is placed in the feedline to the reforming reactor 5. The preferred operating temperaturesand pressures are fixed by the process requirements for effecting thereforming reaction; that is, whether the reaction is effected byexclusively thermal means or with the aid1 of a suitable reformingcatalyst. In order to suppress carbon formation during the'reformingreaction, hydrogen may be admitted with the charge stock, for example,through line 7 in controlled amounts determined by valve 8. Such mixedhydrogen-hydrocarbon feed stocks are particularly desirable when thereforming reaction is effected in the presence of a catalyst such as ametal selected from group VIII of the periodic table supported ou aninert or acidic support, such as platinum or palladium deposited onalumina containing a. small amount of combined halogen, or an iron,nickel and/ or cobalt metal or metal oxide, deposited on alumina oronwalumina-silica composite. Other suitable catalysts include the groupVI metal or metal oxides composited with an inert support such asalumina, including, for example, chromia-alumina composites,molybdena-alumina composites, etc. Following the required period ofresidence of the feed stock in reforming reactor 5, during which timethe naphthenic hydrocarbon components ofthe feed stock undergodehydrogenation and isomerization reactions to form, `in part,` thcanalogous aromatic hydrocarbons therefrom, the products are removed fromreactor through line 9 and thereafter discharged into fractionaldistillation column 10.. Because of the vequilibrium relationshipsbetween the aromatic and naphthenic hydrocarbon components of the feedstockl and the resulting incomplete conversionof naphthenes to theyanalogous aromatichydrocarbons, the product of the reforming 4' @estivacontains @appreciable quantity 0f unconverted naphthenes, which in thecase of benzene production, may. consist of methylcyclopentane,cyclohexane, and polyalkylated cyclopentanes which form benzene bydehydrogenation and isomerization, and which may be accompanied bycracking of one or more alkyl groups from the cyclopentyl nucleus. Inthe case of the ultimate production of toluene from the naphthenichydrocarbon feed stock, the toluene precursors may consist ofdimethylcyclopentane, methylcyclohexane and otherpolyalliylcyclopentanes and cyclohexancs. The naphthcnic precursors ofxylene may consist of trialkylcyclopentanes and diandpolyalkylcyclohexanes. These hydrocarbons may be present individually orin admixture 'in the hydrocarbon feed stock, depending upon the boilingpoint range of the latter; the product of the reforming reaction maytherefore contain benzene, toluene, xyleneand polyalltyl-substitutedjbenzencseither individually or 'in adm ixture,vas well as theunconverted naphthene precursors.

The reforming reaction product charged into fraction.- ator 10 ispreferably segregated into select fractions whose boilingV ranges dependupon the product desired in the presentjprocess. Thus, when the aromaticprimaryproduct to be recovered is benzene, a fraction boiling up toabout 200 F. is separated from the reforming reaction product infractionator 10 and thereafter utilized as feed stock in the subsequentstages of the present process. If the desired primary product istoluene, and only toluene, a fraction boiling from 200 to 270 F. isseparated in fractionator10. A correspondingly higher end point boilingfraction for recovery of xylene or a broad boiling rangefraction,boiling up to about 300 F. for theV recovery of a mixture of aromatichydrocarbons, including benzene, toluene and Xylene, may be selected asa sidecut from fractionator 10 for use as feed to the subsequentextraction stage of the process. One or more of these fractions maybeseparated in fractionator 10 as side-cuts, removed from the columnthrough side-cut draw-offs,` such as line 11. The light gaseouscomponents of the reformed product, such as recycle hydrogen may beremoved from fractionator 10 through line 12 and valve 13 while thebottoms comprising material boiling above the end point of therdesiredside cut is removed from column 10 through lineA 14 and valve 15 tostorageor other disposition.` Heat required for the fractionation may besupplied by means of reboiler 16.

The side-cut to be utilized as feed stock in the subsequent extractionstages of the process, removed from column`10-through line 11, istransferred by `means of pump 17 in. theliquid phase through line 18 inamounts controlled by valve 19 into primary solvent extraction zone 20 for effecting thedesired separation of unconverted naphthenes from thearomatic primary product. A suitable selective solvent for the aromaticand naphthenic components of the feed stock, generally of higher densitythan the hydrocarbon feed, is introduced into the upper portion ofextraction zone 20 through line 21, the solvent generally consisting ofthe lean, regenerated solvent recycled from subsequent stages oftheprocess. Make-up portions of the solvent, designed to replace losses ofsolvent from the system, may be introduced into the processow fromstorage through line 22 in controlled amounts determined by'valve 23.The particular solvent composition for use in the present process isselected on the basis of its selective solvent action for the aromaticcomponent of the feed stock, a more limited solvency for the 'naphthenichydrocarbon components, -and the least solvency foraliphatic hydrocarboncomponents of the mixture. Solvents of this type may be selected from awidevariety of, organic compounds, including the alcohols, glycols,polygly'cols, .glycol,ethers, alcohol esters of Y organic acids, certainorganicA nitriles. and others well 'y toward aromatichydrocarbons'.

recognized inL theA solvent extraction, art for their selectivityv Theselectivity of the solvent for aromatic hydrocarbons may. be enhanced bythe inclusion of an anti-solvent, suchv as water, in the composition,the latter further reducing the solubility of non-aromatic hydrocarbonsinthe solvent. One of the preferred classes of such selective solventsare the glycols and the polyalkylene glycols containing from about 0.5to about 25%, and preferably from 2 to about 10% by weight of water,such as ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, propylene glycol, dipropylene glycol, mixtures ofone or more of the aforesaid glycols or the mixed ether-glycols, such astrimethyl ether of glycerol.

The mixed hydrocarbon feed stock is introduced into extraction zone 20below the point of introduction of the solvent composition and ilowsupwardly in countercurrent relationship to theV more dense solvent,v thearomatic hydrocarbon components of the feed stock being removedtherefrom by the selective solvent action of the solvent in contacttherewith. Under the counter-y current contacting conditions maintainedin the column the solvent becomes progressively richer in aromaticcomponents and leaner in paratlinic components of the feed stock, whichmay initially tend to dissolve in the solvent as a result of theinitially low concentration of aromatic hydrocarbons therein. Althoughthe solvent tends to dissolve aromatic hydrocarbons more readily thannaphthenes, and naphthenic hydrocarbons more readily than aliphatichydrocarbons, and although the aromatics and naphthenes tend to displaceparafns from the solvent, a small proportion of the paratins containedin the mixed hydrocarbon feed stock remain dissolved in the fat solventstream leaving the bottom of the extraction zone, unless such paraniccomponents are completely displaced therefrom by a stream of sucharomatic and/or naphthenic hydrocarbons contacted with the fat solventjust prior to removal of the latter from the extraction zone. In orderto effect such displacement of aliphatic hydrocarbons from the fatsolvent stream a reilux stream containing such aromatic and/ornaphthenic hydrocarbons is introduced into the lower portion of theprimary extraction zone 20 and countercurrently contacted with the fatsolvent stream just prior to'its removal from the extraction zone,thereby displacing the dissolved parains into the railinate flowing fromthe top of the column. The reflux stream, derived from a recycleyfraction as hereinafter indicated, is introduced into the extractionzone, preferably in the lowermost portion thereof, in order to providethe greatest countercurrent contact in the extractor with the fatsolvent stream. By virtue of such selective displacement action ofaromatic and naphthenic hydrocarbons on the parains normally dissolvedin small amounts in the fat solvent, the parainic contaminants aredisplaced into the rising hydrocarbon rainate stream removed from theuppermost portion of the extraction zone through line 24 and valve 25.,In order to provide the aforementioned countercurrent contacting actionbetween the hydrocarbon feed and solvent and the displacement action inthe lower portion of the extraction zone, the feed stock mixture isgenerally introduced into the column between the points of removal ofthe parallinate at the top of the column and the extract phase at thebottom of the extraction zone, the reliux stream being charged into theextraction zone at a point just above the outlet port of the fat solventstream. The fat solvent or extract phase containing the aromatic andnaphthenic hydrocarbon components dissolved in the solvent is removedfrom the extraction zoney through line 26 and is transferred by means ofpump 27 and line 28 in controlled amounts determined by valve 29, intothe upper portion of fat solvent stripping column30, wherein thehydrocarbon solute components ofthe fat solvent stream are vaporizedtherefrom by-distillation with heat supplied to the stripping column'byreboiler 31 or by a jet of steam, not illustrated, introduced into thecolumn. The presence of the solvent inthe stripping zone tends toincrease the boiling point of the aromatic component dissolved thereinrelative to the naphthenic components and in order to provide a fatsolvent residue containing only dissolved aromatic hydrocarbons forsubsequent vaporization from the residue in pure form, suticient heat isintroduced into the fat solvent stream to strip the latter completely ofnon-aromatic hydrocarbons prior to vaporization of the aromatic solutetherefrom. In thus stripping the non-aromatic solute from the fatsolvent, however, a portion of the aromatic dissolved in the fat solventnecessarily distill over the light vapor overhead before the fat solventresidue is free of non-aromatic solute components because of the partialvapor pressure of these aromatics. The aromatic components, free ofnon-aromatic hydrocarbons, `are removed from zone 30 as a side-cutthrough line 32 and valve 33 into storage or for further treatment, notillustrated. In the case of a feed stream to the solvent extraction zonecontaining a mixture of homologous aromatic hydrocarbons, a greaterproportion of the more volatile aromatic component, such as benzene,will be distilled out of the fat solvent in the light'overhead vapor,and a greater proportion of the homologous aromatic, such as toluene andxylene, will be stripped from the fat solvent as the side-cut product.The solvent residue from which the aromatic solute components have beenmore or less completely vaporized is removed as a bottoms stream fromthe lower portion of stripping zone 30 through line 34 and istransferred by meansV of pump 35 into regenerated solvent recycle line21 for reuse as lean solvent in extraction zone 20.

The light vapor overhead stripped from the fat sol'- vent and containingall of the non-aromatic as Well as a` portion of the aromatic componentsof the `fat solvent stream is removed from zone 30 through line 36containing valve 37 and introduced into fractionating column 38 forseparation of the aromatic and non-aromatic components of this stream.In. the absence of the solvent which normally would otherwise increasethe boiling point of the aromatic hydrocarbon component if distilled inits presence, the naphthenic and aromatic hydrocarbons present in theessentially hydrocarbon lightvapor overhead boil at their normal boilingpoints,ror at the boiling point of the azeotrope thereof, making a pre-rliminary partial separation between the aromatic and naphthenes feasibleby fractional distillation. Because of the presence of naphthenes of thesame number of carbon atoms as the aromatic present in the light vaporoverhead, however, the lightest fraction distilled from the hydrocarbonmixture is an azeotropic mixture of the lightest aromatic, and theanalogous naphthenic components present in the overhead. The overheadfrom fractional distillation column 38 is, however, richer in naphthenesthanrthe equilibrium mixture remaining in the column, the aromaticstending to concentrate through loss of overhead naphthenes in the higherboiling residue within column 38. The latter residue, heated by reboiler39, and containing a major proportion of the aromatics charged intocolumn 38, provides a desirable source of hydrocarbon reflux toextraction zone 20, the use of column 38 bottoms as the latter refluxstream -also providing a means of recovering the aromatic componentsinthe system. The aromatics ultimately recovered from the `fat solventstream formed in zone 20 also recover the aromatics present in thearomatic bot-- aromaticsmwhich distill over from column 38, in thef'ofthe solventhasan azeotropic mixture, the overheadvapors beingremoved-from column 38through Enel and valve 45 and` transferred bymeans of pump A16am! line 47 into secondary `extraction zone 48.Selective solvent extraction of the jsecondary overhead in zolle.A inaccordance with this invention eiects the separation of the naphthenicfrom the aromatic cornponents of this `fraction and thereby provides ameans ofrecovering the naphthenic concentrate of this process. Solventextraction asa method ofsegregating the aromatic from the naphtheniccomponents of the secondary overhead provides the most Yconvenient andreadily operable means for effecting such separation be-j causeof Ytherelative solubilities of the two classes of hydrocarbons Ain thesolvent, the solubility of the aromatic componentsLcomprising thesecondary overhead displacing ,heavier naphthenes, and parafns containedin the feedstock from thefat solvent inthe lower portion ofextractionAzonel20. The portion ofnaphthenic product reserved forV use as vrefluxis `removed from product line l through line 53 in controlledjamountsdetermined by valye 54 and i`sk Vtransferred by means of pump 55 intoline 56 VfromV which' the reflux portionis removed through line57andvalve S8 for discharge into primary extractionV zone 20.l Thereflux stream .is preferably charged into thelowermosttray of zone 20,immediately above the fat solvent outlet, in order to accomplishcountercurrent Contact with the fat solvent stream just prior to removalof the latterfrom the extraction zone and transirf the solvent beingsubstantially greater than the naph- `hydrocarbon components. Therefore,the mere contact of the secondary overhead with the selective solvent,preferably in a countercurrent ow arrangement, will form a fat solventstream containing the aromatic components and a rainate streamconsisting substantially ofpure naphthenic product. Any naphthenesdissolving fthe secondary fat solvent are returned to the process`tlow,"and,thereby ultimately recovered because of the provision hereinfor recycling the secondary fat solvent streamto `the primary fatsolvent stripping column.V The solvent for the secondary extraction zone48 may be the same, as or `different from the`solvent utilized inprimary extraction Azone 20 and is preferably the same solventto enablea single fat solvent stripping column to( be `utilized for both theprimary andsecondary fat solvent streams,` the product recovered fromboth streams being the aromatic component of'the feedstock.

`Apreferred arrangement for this purposeis to 4utilize the regeneratedsolvent recovered as the lean solvent stream from stripping column asthe source of `lean solvent for secondary extractor 48, Yandforthis'purpose a side stream of solvent is removed frorn regeneratedsolvent return line 21 and'is thereafter transferred `by pnmpintosecondary solvent feed line 49 in controlled amounts `determined byvalve 50. The solvent stream is conducted in to the upper portionofsecondary extraction zone 48, and' permitted to flow downwardly` incountercurrent relation shop to the rising hydrocarbon stream introducedinto zone 48 through line 47. The secondary overhead stream comprisingthe feed to extraction zone 48 is admitted into `column 48 at a pointsubstantially below thesolvent inlet and preferably in thelowermostportion' of the column. The naphthenic hydrocarbon component orcomponents, constituting the lightest naphthenes present in the initial`feed stock do not dissolve to any vsubstantial degree in the `presenceof aromatic hydrocarbon in the solvent and therefore may be removed fromthe upper portion of zone 48` as a rainate stream through line 51 andvalve 52 to product storage or for further fractionation to separate4individual naphthenes therefrom. The aromatic hydrocarbons whichselectively dissolve in the solvent stream charged into secondaryextractor 48 may be recovered from the resulting fat solvent in asecondary stripper,rnot illustrated,

`but preferably are recovered with the aromatics present in the primaryfat solvent stream in stripper 30; for this purpose thefat solvent fromthe secondary extractor 48 is! removed through line 51' and valve 52 andcharged into line 26 leading to stripper 30. `The aromatic pro-V ductstream removedthrough line- 32 from stripper 30 thereby contains all thearomatics present inthe sys-l portion ofthe naphthenic product `asareflux stream in primaryfextraction zone 20, thel lightlnaphthenicwproduct The Vnaphthenic hydrocarbon recovered fromsecondary; extraction Vzone 48 through line 51 consists of substantiallyfer to the strippingrcolumn., Bythns contacting the fat solvent streamwith the light naphthenes just prior to stripping the fat solvent,maximum effective displacement of heavy naphthenes and parains isthereby accomplished.

When the ultimate purpose of the present process is the conversion ofnaphthenes to aromatic hydrocarbons in the aforementioned Vreformingstage, rather than the recovery of a substantially pure naphthenichydrocarbon product, the naphthenes removed from product line 51throughline 53 may be transferred by means of pump 55 through line 56and valve 59 into line 1 which feeds into reforming reactor 5, wherebythe naphthene to aromatic molar ratio inthe reforming zone is increased,likewise increasing the conversion of naphthenes to aro-` matics.; Bymanipulation of valve 58 and 59, either a minor proportion or a majorproportion of the naphthenic product may be either recycled to thereforming 'reactor or returned to the vprimary extraction zone as a reuxstream therein. It is to be noted however that at least a portion of thelight naphthenes recovered as product must be diverted into line 57 foruse as reflux in order to obtain the aforementioned selectivedisplacement of heavy naphthenes and parains from the primary fatsolvent stream.r Since both the aromatics and light naphthenes areuseful as a source of reflux in the primary ex-` traction zone todisplace heavy parailins and naphthenes fromjthefat solvent prior tostripping, an alternate supply of the reflux stream which contains bothof said aromatic and naphthenic components is the light overhead fromthe stripping zone,`the latter being` recycled to reflux line 53 .fromoverhead line 36 through conduit 60, the amount thereof being controlledby valve 61.

Other modifications of the process are obviously feasible and thepreferred method of operation which is se. lected herein forillustrative purposes only in the following example isnot intended tolimit the generally broad scope of the invention in strict accordancetherewith.

Example A naphthene-base petroleum stock boiling from an initialboilingpoint of4 about 65 F., up to an end boiling pointfof about 400 F. andcontaining the following classes Aof hydrocarbons in their indicatedproportions:

. Percent Paratfins, 63 Olens 1 Naphthenes Y 28 Aromatics L--- 8.3

` forming `reaction. f The conversion of f naphthenic` to aromatichydrocarbons is anequilibrium conversion which-lis determined atleast inpart by the concentration ofLla'ron'latiesl -intheefeed stock-to thePlatformingreaetor:

9 The reformed product .contains the following classes of hydrocarbonsin their indicated proportions:

The normally liquid portion of the product is subjected to solventextraction under countercurrent ow conditions in a column into which thefeedstock is introduced on approximately the center plate of the column,the solvent, consisting of a 7.5% aqueous solution of diethylene glycol,being charged onto the top tray of the column and allowed to percolatedownwardly through the column against the rising stream of liquidhydrocarbon feed stock. A rainate stream composed almost exclusively ofthe paraflinic components of the feed stock is removed from the top trayof the column and discharged from the process ow. The naphthenes presentin the rallnate, as shown by analysis of this stream were C7, Cs, andhigher molecular weight alkylcyclohexanes and cycloheptanes, there beingsubstantially no Cyclopentane, methylcyclopentane or cyclohexane presentin -this stream.

A reflux fraction comprising Cyclopentane, methylcyclopentane andcyclohexane, recovered as a product stream in the subsequent stages ofthe process, as hereinafter indicated, was charged into the bottom ofthe extraction column at a rate of approximately 8% by volume of thecharging stock feed rate.

A fat solvent stream removed from the bottom of the extraction column ata temperature of 280 F. and at a pressure of 90 p. s. i. g. was fed intoa fat solvent stripper comprising a fractional distillation columncontaining a reboiler, and a steam inlet on the lowermost tray intowhich steam at 20 pounds pressure was admitted for the purpose ofstripping the last traces of hydrocarbon solute from the fat solvent.The stripper operates at essentially atmospheric pressure, except-thatthe uppermost trays containing liquid seals between successive plates,were operated at successively reduced pressures from a maximum of 90 p.s. i. g. on the uppermost tray. An overhead vapor stream containing 35%-by Vvolume of aromatics (predominantlybenzene)and 65% by volume of lightnaphthenes (Cyclopentane, ,methylcyclopentane and cyclohexane) wasremoved from the top of the stripper and discharged in vapor state intoa fractional distillation column. A side stream removed from a lowertray of the stripper consisted of water, benzene, toluene and xylene,the hydrocarbon content of which was 99.9% aromatic. A regenerated leansolvent stream, reconstituted to 7.5% water was pumped from the reboilersection of the stripper to the top of the primary extraction column, asmall side-stream being separately removed for diversion to a secondaryextractioncolumn, hereinafterdescribed. y v

The stripper overhead when fractionally distilled yielded a fractionatoroverheadv consisting predominantly of benzene and about 38% by volume ofa mixture of cyclopentane, methylcyclopentane and cyclohexane. Thebottoms from the column contained no naphthenes and was composedprimarily of benzene, toluene and xylene which was recycled as a refluxstream to a lower plate of the primary extraction column, beingintroduced into the column into an inlet approximately two plates abovethe inlet for the light naphthene reilux which was introduced into thebottom of the primary extraction column and which was derived by furtherextraction of the fractionator overhead, as hereinafter described.

The napthenic-aromatic hydrocarbon fractionator overhead was chargedinto the bottom of a secondary extraction column of similar design butof substantially smaller size than the primary extractor. The rainatestream from the top of the column upon analysis contains no 'f1-0'aromatic components and contains none of the heavy naphthenes present inthe initial feed stock. The small bleed stream of regenerated glycolsolvent removed from the bottom of the stripper was charged into the topof the secondary extractor and allowed to dow downwardly therein,countercurrent to the liquid phase hydrocarbon mixturej(fractionatoroverhead). A fat solvent stream removed from the bottom of the secondaryextractor contained the aromatic components present in the fractionatoroverhead, that is, all of the benzene distilled overhead with the lightnaphthenes from the fractionator. A small amount, (approximately 12% ofthe total hydrocarbon solute presentin the fat solvent stream) of lightnaphthenes was also dissolved in the secondary extractor fat solventstream. The latter stream was pumped into the supply line leading intothe primary fat solvent stripper.

The light naphthenes contained in tihe secondary extractor. rainatestream contained no aromatic or parafnic components and its analysisindicated that it is made up of approximately the following amounts ofeach of the indicated light naphthenes:

Percent Cyclopentane About 65 Methylcyclopentane About 22 CyclohexaneAbout 13 reactor for use therein as supplement for the feed stock to theprocess, which thereby increases the total conversion of naphthenes toaromatic product (benzene) by displacement of the naphthene-to-benzeneequilibrium in the reforming reaction zone.

We claim as our invention:

l. In a process for separating in a counter-current primary solventextraction zone a-mixture of hydrocarbons comprising paraifinic,naphthenic and aromatic components, employing a solvent more dense thansaid mixture and in which the naphthenic and aromatic components areatleast partially-soluble, removing from the lower portion of said Vzonea'primary fat solvent stream, and removing from the upper portion ofsaid zone a raffinatepcomprising the'paratlinic components of saidmixture,f the method which comprises introducing said mixture into saidzone at a point between the raffinate and fat solvent outlets of saidzone, vaporizing from said primary fat solvent a light overheadcomprising aromatic and naphthenic hydrocarbon components of saidmixture, subjecting at least a portion of said overhead to solventextraction in a secondary extraction zone and therein separatingnaphthenic fromV aromatic cornponents, recovering a secondary rainatefrom said secondary zone comprising the relatively low molecular weightnaphthenic components of said mixture, and recycling a rellux streamselected from the group consisting of (l) a portion of said secondaryraiinate and (2) a portion of said light overhead to said primaryextraction zone, and introducing said retlux into said primaryextraction zone below the inlet of said mixture therein.

2. In a process for separating in a counter-current primary solventextraction zone a mixture of hydrocarbons comprising paranic, naphthenicand aromatic cornponents, employing a solvent more dense than saidmixture and in which the naphthenic and aromatic components are at leastpartially soluble, removing from the lower portion of said zone aprimary fat solvent stream and removing from ,the upper portion of saidavsaoge'ao zone a raffinate comprising the `pararinic components ofsaid` mixture, the method whichJ comprises introducing said mixtureintosaid zone'ata point between theraffnate and fat solvent outletsoffsaidzone, vaporizing from said primary fat solvent in a vaporizingzonealight overhead comprising aromatic "andnaphthenic hydrocarboncomponents vrof said mixture, segregating atleast a portion ofsaidoverhead and subjectingsaid portion t solvent extraction in asecondary extraction zone and therein separating naphthenic fromaromatic components, recovering aV secondary raffinate stream from saidsecondary zonecomprising the relatively low molecular weight naphthenichydrocarbon components `of saidmixmre, recovering a secondary fatsolventasfbottoms from said secondaryextraction zone `and supplying vthesame to saidvaporizing zone, and` recycling a reflux stream selectedfrom the group. consisting ofY (l) aportion of said secondary rallinateand V(2) a portion of said light overhead to said primary extractionzone, and introducing said reux into said 'primary extraction zone belowthe inlet of said mixture therein.`

3. The process of claim 1 further characterized in that said mixture of`hydrocarbons contains a C6 naphthenic hydrocarbon.

4; The process of claim l furthercharacterized in that said mixture ofhydrocarbons contains C5 naphthenic and C5 aromatic hydrocarbons.

5. The process of claim'l further characterized by introducing saidmixture at approximately the mid-point and said reux stream intoapproximately the` bottoni of: said primary extraction zone. t

6. The process of. claim l further characterized in that said lightoverhead isfractionated to segregate a relatively volatile fractioncomprising a naphthenic hydrocarbonV component `of said mixture from valess: volatile fraction comprising an` aromatic hydrocarbon componentofsaid mixture, recycling `said less volatile fraction to said primaryextraction zone as a` reux stream, and introducing said reflux into thelower portion of said primary zone. 1 t

7. The process of claim 1 further characterized by fractionating, saidlight overhead fraction to segregate a relatively volatile fractioncomprising fa naphthenic hydrocarbon component of said mixturelfrom aless volatile fraction' comprising an aromatic hydrocarbon componentV ofsaid mixture, recycling at least a portion of `said relatively yvolatile`fraction to said primary extraction `zone as a vreliu'x stream,andintroducing said retluxi into the lower portion of said primary zone.

8. A process for the conversion of naphthenic hydrocarbons to yaromatichydrocarbons which comprises subjecting a hydrocarbon mixturecomprisinga naphthenic hydrocarbon precursor of said aromatic hydrocarbon `toreforming conditions whereby said naphthenic hydrocarbon converted to an`equilibrium mixture of aromatic and naphthenic hydrocarbons, subjectingthe product of said reforming stepto solvent extraction in a primaryextraction zone with `a solvent more dense than said mixture and inwhich the naphthenicand aromatic components arel atleast partially.soluble, `removing from thelower portion of the extraction zone aprimary fat solvent. stream, removing. a rainate comprising the parainiccomponents of said` mixture from the upper portion ofsaid zone,introducing. said mixture into the extraction zone at apointbetween..the raiinate and fat solvent outlets of said zone, vaporizingfrom said primary fat solvent a light overhead comprising aromatic andnaphthenic hydrocarbon components of said mixture, segregating at leasta portion` of said overheadand subjecting said portion to solventextraction in a secondary extraction zone and therein separatingnaphthenic from aromatic components, recovering a secondary rafiinatestream fromsaid secondary zone comprising the relatively low molecularweight' naphthenic hydrocarbon components of said mixture, recycling areflux stream selected fromV the group consisting of (1) a portionofsaid secondary rainate and (2) a portion of said light overhead to saidprimary extraction zone, introducing said reflux into said primaryextraction zone below the inlet of said mixture' therein, and recyclinga portion of said secondaryrafnate to said reforming step.

9. A process for recovering a naphthene concentrate from a mixture ofparainic, naphthenic and aromatic hydrocarbons whichcomprisescountercurrently contacting said mixture in a primaryextraction zone with a solvent more dense than said mixture and in whichthe naphthenic and aromatic hydrocarbons are at least partially soluble,removing `the resultant fat` solvent from the lower portion of said zoneand 'vaporizing aromatic and naphthenic hydrocarbons therefrom in astripping zone, fractionating the resultant vapors to separate the sameinto relatively llight and heavy fractions, introducing the heavierfraction to the lower portion of said primary zone as reflux therein,subjecting the lighter fraction to solvent extraction in a secondaryextraction zone with a solvent for aromaticsto separate the naphthenicfrom the aromatic components of the lighter fraction, andV supplying thefat solvent from said'secondary zone tosaid stripping zone forvaporization of the dissolved aromatics therein.

10. The process of claim V9 further characterized in that there isVrecoveredas aV iside-cut from said stripping zone an aromatic productofhigher boiling point thansaid vaporsV from the stripping zone.

11.7The process of claim 9 further characterized in that separatestreams of lean solvent from said stripping zone are introduced to theupper portions of said primary and secondary extraction zones.

References Cited-in the lc ofthis patent UNITED STATES PATENTS

1. IN A PROCESS FOR SEPARATING IN A COUNTER-CURRENT PRIMARY SOLVENTEXTRACTION ZONE A MIXTURE OF HYDROCARBONS COMPRISING PARAFFINIC,NAPHTHENIC AND AROMATIC MIXPONENTS, EMPLOYING A SOLVENT MORE DENSE THANSAID MIX TURE AND IN WHICH THE NAPHTHENIC AND AROMATIC COMPONENTS ARE ATLEAST PARTIALLY SOLUBLE, REMOVING FROM THE LOWER PORTION OF SAID ZONE APRIMARY FAT SOLVENT STREAM, AND REMOVING FROM THE UPPER PORTION OF SAIDZONE A RAFFINATE COMPRISING THE PARAFFINIC COMPONENTS OF SAID MIXTURE,THE METHOD WHICH COMPRISES INTRODUCING SAID MIXTURE INTO SAID ZONE AT APOINT BETWEEN THE RAFFINATE AND FAT SOLVENT OUTLETS OF SAID ZONE,VAPORIZING FROM SAID PRIMARY FAT SOLVENT A LIGHT OVERHEAD COMPRISINGAROMATIC AND NAPHTHENIC HYDROCARBON COMPONENTS OF SAID MIXTURE,SUBJECTING AT LEAST A PORTION OF SAID OVERHEAD TO SOLVENT EXTRACTION INA SECONDARY EXTRACTION ZONE AND THEREIN SEPARATING NAPHTHENIC FROMAROMATIC COMPONENTS, RECOVERING A SECONDARY RAFFINATE FROM SAIDSECONDARY ZONE COMPRISING THE RELATIVELY LOW MOLECULAR WEIGHT NAPHTHENICCOMPONENTS OF SAID MIXTURE, AND RECYCLING A REFLUX STREAM SELECT ED FROMTHE GROUP CONSISTING OF (1) A PORTION OF SAID SECONDARY RAFFINATE AND(2) A PORTION OF SAID LIGHT OVERHEAD TO SAID PRIMARY EXTRACTION ZONE,AND INTRODUCING SAID REFLUX INTO SAID PRIMARY EXTRACTION ZONE BELOW THEINLET OF SAID MIXTURE THEREIN.